1. Field of the Invention
The present invention relates to a method of fabricating a semiconductor light-emitting device and the semiconductor light-emitting device obtained by such method, and in particular to a method of fabricating a semiconductor device having on a substrate a multi-layered film which includes an active layer, and the semiconductor light-emitting device obtained by such method.
2. Description of the Related Art
An optical pickup used for read/write (record/playback) to or from optical recording media such as CD (compact disc) and DVD (digital versatile disc) incorporates a semiconductor light-emitting device.
An exemplary constitution of such semiconductor light-emitting device is shown in FIG. 7A and FIG. 7B, which are a plan view and a sectional view taken along the line VIIBxe2x80x94VIIB in FIG. 7A, respectively. The semiconductor device shown in these figures has on a single substrate 101 a first semiconductor laser element L101 and a second semiconductor laser element L201, both elements being differed in the emission wavelength. The semiconductor laser elements L101, L201 are respectively composed of multi-layered film patterns P101, P201 which individually comprise lower clad layers 102, 202, active layers 103, 203 individually having a quantum well structure, and upper clad layers 104, 204 individually having a conduction type different from that of the lower clad layers 102, 202, all of which are stacked in this order; and current injection layers 105, 205 individually formed thereon.
In a fabrication process of such semiconductor light-emitting device, at first a multi-layered film made of AlGaAs-base (aluminum gallium arsenide-base) material for composing the first semiconductor laser element L101 is epitaxially grown on the substrate 101 made of, for example, GaAs (gallium arsenide). The multi-layered film is then patterned to form a plurality of the first multi-layered film patterns P101 spaced in a predetermined distance apart from each other. Here the individual first multi-layered film patterns P101 have a uniform line width of approximately 150 xcexcm. A multi-layered film made of AlGaInP-base (aluminum-gallium-indium-phosphorus-base) material for composing the second semiconductor laser element L201 is epitaxially grown on the substrate 101 and is then patterned to form a plurality of the second multi-layered film patterns P201 of a constant width between each adjacent first multi-layered film patterns P101.
Next, the top epitaxial layers of the individual multi-layered film patterns P101, P201 are patterned to form the first current injection layer 105 on the top of the first multi-layered film pattern P101 and, likewise, to form the second current injection layer 205 on the top of the second multi-layered film pattern P201 so as to extend along the longitudinal direction of the both patterns P101, P201, respectively. This forms current bottlenecking layers 103a, 203a (so-called stripes) in the individual active layers 103, 203 in the respective multi-layered film patterns P101, P201. The substrate 101 is then divided in a pair of the first multi-layered film pattern P101 and the second multi-layered film pattern P201 formed thereon, and the multi-layered film patterns P101, P201 and the substrate 101 are then cleft en bloc in a plane normal to their longitudinal direction. Thus, a semiconductor light-emitting device having on a single substrate 101 the semiconductor laser elements L102, L201 differing in the emission wavelength is obtained.
In the thus obtained semiconductor light-emitting device, the active layers 103, 203 have a resonation structure by having cleft planes on both ends of the multi-layered film patterns P101, P202, so that light emitted from the active layers 103, 203 can be resonated and drawn out through such cleft planes.
However, the semiconductor light-emitting device having such constitution is disadvantageous in that the band gap of the active layers 103, 203 becomes smaller in the vicinity of the cleft planes than in the central portion due to interfacial levels, poor heat conduction and large light density in the vicinity of the cleft planes. Hence, in the semiconductor laser element composed of an AlGaInP-base material, light generated at around the central portion of the stripe 203a is likely to be absorbed in the vicinity of the cleft planes, which undesirably increases an amount of heat generation, limits a maximum oscillation output and induces fracture of the cleft planes.
To overcome the foregoing problems, a so-called window structure capable of expanding the band gap in the vicinity of the cleft planes of the active layer is provided. Semiconductor light-emitting devices based on such window structure are roughly classified into those having the multi-layered film pattern whose cleft plane sides are filled with a large-band-gap material, and those having the multi-layered film pattern in which impurity is diffused in the vicinity of cleft planes so as to destroy the super lattice structure of the active plane, to thereby expand the band gap.
Fabrication of such window structure, however, requires complicated processes and high-precision process technology, thus increasing the production cost and lowering the yield of the semiconductor light-emitting devices.
For example, in the formation of the semiconductor light-emitting device for emitting red laser light, the active layer is diffused with Zn (zinc) as an impurity in the vicinity of the cleft planes. Zinc, however, tends to produce a non-emissive sensor within the active layer, which is causative of degrading the property and thus compromising the reliability of the device if present in the light-emissive region. For this reason, it is necessary that an amount of zinc diffused within the active layer in the vicinity of the cleft planes is set to be large in order to expand the band gap, but it has to be set at approximately zero in the central area which serves as a light-emissive region. Thus, an advanced process technology is required for precisely controlling the diffusion area and diffusion depth of zinc.
It is therefore an object of the present invention to provide a method of fabricating a semiconductor light-emitting device by which the window structure can readily be obtained without relying upon the advanced technology, and the semiconductor light-emitting device obtained by such method.
A method of fabricating a semiconductor light-emitting device to accomplishing the foregoing objective is a method of fabricating a semiconductor light-emitting device having on a substrate a semiconductor light-emitting element, and being characterized by a procedure as described below. First, a material layer formed on the substrate is patterned to thereby form a groove pattern having a widened portion and narrowed portions provided on both sides of the widened portion, the narrowed portions are provided with openings which are narrower in width that the widened portion. Next, a multi-layered film composed of a lower clad layer, an active layer and an upper clad layer having a conduction type differing from that of the lower clad layer, stacked in this order is formed on the substrate so as to cover the groove pattern. Thereafter, a current injection layer is formed on the multi-layered film within an area corresponding to the groove pattern so as to extend along the longitudinal direction of the groove pattern.
In such fabrication method, since the multi-layered film is formed so as to cover the groove pattern having the widened portion, a thickness of the individual layers composing the multi-layered film formed within the groove pattern is larger in the widened portion than in the narrowed portions provided on both sides thereof. This is attributable to the fact that a larger amount of source materials can be supplied to the widened portion than to the narrowed portion (rate determined by supply volume), and that the source materials supplied to the narrowed portion is likely to be consumed due to abnormal film growth at the upper portion of the etched side wall of the groove pattern. Thus, by patterning such multi-layered film, while aligning the portion thereof formed within the widened portion to the center, and the portions formed on both sides thereof to the edge, a semiconductor light-emitting device can be produced to as to having an active layer in which a film is thinner at both ends than in the center, and therefore having the window structure in which the band gap of the active layer is higher in both edge portions than in the central portion.
A semiconductor light-emitting device of the present invention is such that being obtained as described in the above, wherein a multi-layered film pattern composed of a lower clad layer, an active layer and an upper clad layer having a conduction type different from that of said lower clad layer stacked in this order is formed on a substrate and, on such multi-layered film pattern, a stripe of a current injection layer is provided so as to extend over both edges of the multi-layered film pattern. The active layer thereof is characterized in that being formed so that both end portions thereof along the longitudinal direction of the current injection layer is thinner than the central portion.